1. Field of the Invention
The present invention generally relates to the art of photodetectors, and more specifically to a wideband anti-reflection coating for an indium antimonide (InSb) photodetector which enables detection of light at visible as well as infrared wavelengths.
2.Description of the Related Art
Back-side illuminated InSb photodetector devices such as photodiode arrays are widely used for detecting infrared radiation at wavelengths between approximately 1 and 5.5 microns. InSb has a refractive index on the order of 4.0, and if no anti-reflection coating were provided, approximately 36% of incident light would be lost due to reflection from the light receiving surface. However, anti-reflection coatings are available which reduce the surface reflection to a level which enables practical use of the detectors at infrared wavelengths. A detailed treatise on conventional anti-reflection coatings is presented in a textbook entitled "THIN-FILM OPTICAL FILTERS", by H. Macleod, Adam Lilger, Ltd: London, 1969, pp. 37-72.
InSb devices are sensitive to visible light at wavelengths as short as approximately 0.4 microns as well as to infrared radiation. However, an anti-reflection coating which is effective over the extremely wide wavelength band from 0.4 microns to 5.5 microns has not been available, and this has limited the use of InSb photodetectors to applications for both the visible and infrared spectral regions.